The Object.unobserve() method was used to remove observers set by Object.observe(), but has been deprecated and removed from Browsers. You can use the more general Proxy object instead.
JavaScript is designed on a simple object-based paradigm. An object is a collection of properties, and a property is an association between a name (or key) and a value. A property's value can be a function, in which case the property is known as a method. In addition to objects that are predefined in the browser, you can define your own objects. This chapter describes how to use objects, properties, functions, and methods, and how to create your own objects.
Starting with ECMAScript 2015 (ES6), a shorter syntax for method definitions on objects initializers is introduced. It is a shorthand for a function assigned to the method's name.
The Object.defineProperty() method defines a new property directly on an object, or modifies an existing property on an object, and returns the object.
The Object.entries() method returns an array of a given object's own enumerable property [key, value] pairs, in the same order as that provided by a for...in loop (the difference being that a for-in loop enumerates properties in the prototype chain as well).
The Object.keys() method returns an array of a given object's own enumerable properties, in the same order as that provided by a for...in loop (the difference being that a for-in loop enumerates properties in the prototype chain as well).
The __noSuchMethod__ property used to reference a function to be executed when a non-existent method is called on an object, but this function is no longer available.